Design tokens — refinement to disabled and border colour tokens

[mkernohanbc]

We are intending to make some changes to the design tokens schema to:

• Add a new light border colour
• Refine the colour tokens used to indicate disabled/inactive text and UI elements to make them more legible
• Add a hover colour for hyperlinks (per request from user)
• Add a new 0.75rem token (between medium and small) for padding and margin

These changes should not be breaking, but we will investigate and confirm whether this will be a major or minor release.

[mkernohanbc]

Note: shipping changes to @bcgov/design-tokens is currently blocked by Tokens Studio licensing and #544. We also need to review #516 as part of a putative next release.

@Philip-Cheung if there are other proposed changes or additions to the tokens, please note them here for reference.